Detonating Cord With Protective Jacket

ABSTRACT

This invention relates to a detonating cord ( 10 ) having a core ( 12 ) of reactive material and a composite jacket around the core, and the method of its manufacture. The composite jacket includes an interior jacket ( 14 ) in contact with the core and a sacrificial jacket ( 20 ) disposed over the interior jacket. The sacrificial jacket prevents the cord from being cut off by the detonation of another detonating cord of like core load disposed adjacent thereto. The sacrificial jacket is separable from the interior jacket beneath it under the force of the adjacent detonating cord, thus absorbing energy and allowing the first detonating cord to remain intact. The detonating cord may have a core load of not more than 3.2 grams/meter (15 grains/ft) or, optionally, less than 1.25 g/m (6 grains/ft). The interior jacket may be free of metal jacket layers. Optionally, the outer cross-sectional diameter of the cord may be not more than about 3.8 mm (0.15 inch) so that it can be inserted into a standard detonator. The sacrificial jacket may be made from polyethylene and may have a thickness of about 0.25 mm (0.01 inch).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to detonating cord and, in particular, tolow-energy detonating cord that is not subject to cut-off by a similardetonating cord that functions when in contact therewith.

Detonating cord is well-known in the art of initiating explosive signalsand usually comprises a solid core of explosive material such aspentaerythritol tetranitrate (hereinafter “PETN”) enclosed within asingle- or multilayer-jacket. Some detonating cords comprise a singlelayer jacket, e.g., a single layer of polyethylene extruded over theexplosive core, but typically, the jacket comprises a textile tube indirect contact with the core of explosive materials and one or moreadditional jacket layers thereover to provide the desired tensilestrength, resistance to deactivation by water, and other desiredcharacteristics. Detonating cord has a variety of uses, including thetransmission of a detonation signal along its length from one device toanother. Frequently, on a blasting site, one length of detonating cordmay come in contact with another, either inadvertently or by design.Such inadvertent contact may occur with one section of a length ofdetonating cord with another section of the same cord; at other times itoccurs because one cord must cross over another in order to conveydetonation signals to their respective destinations. Some detonatingcords come into contact by design, e.g., by the tying of a knot betweenthem, so that a signal on one cord can be transferred to another cord.

A common problem with the use of detonating cord in these ways is that,depending on the nature of the contact between them, a first functioningdetonating cord (or section thereof) may “cut off” another length ofdetonating cord, i.e., it may sever the second length of cord withoutinitiating a signal therein. Once severed, the detonating cord isincapable of functioning to convey a detonation signal to its intendedtarget. Cut-off may occur when one length of detonating cord is disposedin close proximity, or in contact, with another in a manner that doesnot permit signal transfer from one cord (or section thereof) toanother. As indicated above, tying a knot between two cords is typicallysufficient to enable signal transfer from one cord to another, butoften, disposing the cords in unknotted, side-by-side relation with eachother, or at an acute angle relative to one another, will cause theoutput from one cord to sever, but not initiate, the other.

2. Related Art

U.S. Pat. No. 3,726,216, issued to Calder, Jr. et al on Apr. 10, 1973,and entitled “Detonation Device and Method For Making the Same”,discloses a detonating cord designed for signal transfer from onesection of such cord to another by tying a knot between them. Theoccurrence of cut-off is reduced so that the cords need not berestricted to mutually perpendicular orientation. This is achievedthrough the use of core material having finely granulated particles. Inthe illustrated embodiment, the explosive core is surrounded by severaljacket layers, including (from inward to outward) an inner layer offibrous layer 54, a textile layer 56, another textile layer 58, amoisture-impervious barrier 60, a textile layer 62, another textilelayer 64 and a water-repellant outer protective layer 66. The PETN corematerial has a fine granulation such that only 15 percent or less byweigh is retained on a 100 mesh sieve (column 5, lines 27-33). The coreloading of such material is in the range of about 15 to 40 grains perfoot (column 5, lines 37-40 and column 8, lines 43-48).

U.S. Pat. No. 3,311,056, issued to Noddin on Mar. 28, 1967, and entitled“Non-Rupturing Detonating Cords”, discloses a detonating cord comprisingan explosive core encased within a polyurethane elastomer sheath. Thepolyurethane sheath may be in direct contact with the core or it may beseparated therefrom by one or more layers of materials such as metal,plastic or fabric (see column 2, lines 46-52). The core loading may befrom 1 to 400 grains per foot (column 3, lines 8-11). The polyurethanedoes not rupture when the cord functions, so the cord will not affectadjacent temperature-sensitive materials (column 3, lines 55-65).

U.S. Pat. No. 2,982,210, issued to Andrew et al on May 2, 1961, andentitled “Connecting Cord”, discloses a cord comprising a crystallinecap-sensitive high explosive core 1 enclosed within a metal sheath 2 ata loading of 0.1 to 2 grains per foot. The metal sheath 2 may or may notbe covered by a non-metallic material 3 such as fabric or plastic (seecolumn 2, lines 48-60). The cord will not initiate or damage anothercord adjacent to it, or an adjacent dynamite cartridge; it can be tiedin knots without interfering in the propagation of the detonation pulseand without a cut-off at the knot (see column 3, lines 35-40), and itcan be used for bottom-hole priming (see column 5, lines 29-35).

U.S. Pat. No. 4,024,817, issued to Calder, Jr. et al on May 24, 1977,and entitled “Elongated Flexible Detonating Device”, discloses adetonating cord 20 having an outer energy-absorbing layer 30 releasablyapplied thereto (see column 9, lines 32-35). The energy-absorbing layer,which may comprise extruded plastic 72, is separated from the detonatingcord therein by an intervening layer of fibrous material 70 such ascotton, rayon or other yarn (see column 9, lines 59-65). Therefore, theenergy-absorbing layer 30 can be stripped from the detonating cordtherein (see column 4, line 67 through column 5, line 3). Theenergy-absorbing layer and the layer of fibrous material 70 serve todampen and reduce the transmitted energy available when the detonatingcord is initiated, to prevent the detonation of explosive material whichis in contact with the energy-absorbing layer 30 (see column 4, lines24-28, lines 46-50 and column 5, lines 6-15). A short length of theenergy-absorbing layer can be removed from the end of the detonatingcord by circumferentially cutting the layer and slipping the severedportion of energy-absorbing layer off the end of the detonating cord(see column 10, lines 31-36).

SUMMARY OF THE INVENTION

This invention relates to a detonating cord comprising a core ofreactive material and a composite jacket around the core. The compositejacket comprises an interior jacket surrounding the core and in contacttherewith, and comprising an outermost interior jacket layer and asacrificial jacket disposed over the interior jacket, the sacrificialjacket being separable from the interior jacket in response to thedetonation of an adjacent similar section of detonating cord and beingeffective to prevent the cord from being cut off by the adjacent similarsection of detonating cord.

According to one aspect of the invention, the detonating cord may have acore load of less than about 3.2 grams/meter (g/m) (15 grains per foot(grains/ft)) or, optionally, less than 1.25 g/m (6 grains/ft).Alternatively, the detonating cord may have a core load in the range ofabout 0.2 to 2 g/m (1 to 10 grains/ft) or, optionally, in the range offrom about 1 to 1.5 g/m (5 to 7 grains/ft).

According to another aspect of the invention, the outer cross-sectionaldiameter of the cord may be not greater than about 3.8 millimeter (mm)(0.15 inch).

According to still another aspect of the invention, the interior jacketmay be free of metal jacket layers.

According to still another aspect of the invention, the sacrificialjacket may comprise a sacrificial textile layer woven over the interiorjacket and a sacrificial extruded layer extruded over the sacrificialtextile layer. Optionally, the sacrificial extruded layer may comprise alayer of polyethylene having a thickness of about 0.25 mm (0.01 inch).

In other embodiments of the invention, the sacrificial jacket maycomprise a sacrificial extruded layer disposed directly onto theinterior jacket. Optionally, the outermost interior jacket layer and thesacrificial jacket may comprise mutually compatible polymeric materials.For example, the sacrificial extruded layer and the outermost interiorjacket layer may both comprise polyethylene and the thickness of thesacrificial extruded layer has a thickness of about 0.01 inch.Alternatively, the outermost interior jacket layer and the sacrificialjacket may comprise mutually incompatible polymeric materials.

This invention also relates to a method for making a detonating cord,comprising disposing an interior jacket around a core of explosivematerial, the interior jacket comprising at least an outermost interiorjacket layer, the interior jacket being insufficient to protect thedetonating, cord against cut-off by the initiation of an adjacentsimilar section of detonating cord, and disposing a sacrificial jacketover the interior jacket.

The method may comprise extruding the sacrificial jacket onto theinterior jacket, wherein the sacrificial jacket and the outermostinterior jacket layer comprise polymeric materials that are mutuallycompatible, and cooling the interior jacket before extruding thesacrificial jacket onto it.

Optionally, the method may comprise extruding the sacrificial jacketonto the interior jacket, wherein the sacrificial jacket and theoutermost interior jacket layer comprise mutually incompatible polymericmaterials.

In one embodiment, disposing the sacrificial jacket around the interiorjacket may comprise forming a sacrificial textile layer over theinterior jacket and extruding a sacrificial extruded layer onto thesacrificial textile layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, cross-sectional view of a detonating cordaccording to one particular embodiment of the present invention;

FIG. 2 is a schematic elevation view of the detonating cord of FIG. 1after the functioning of an adjacent similar detonating cord;

FIG. 3 is a flow chart that schematically illustrates one method formaking detonating cord having a sacrificial jacket;

FIG. 4 is a flow chart that schematically illustrates another method formaking detonating cord having a sacrificial jacket;

FIG. 5 is a schematic cross-sectional view of a detonating cordaccording to another embodiment of the invention;

FIG. 6 is a flow chart that schematically illustrates another method formaking detonating cord having a sacrificial jacket; and

FIGS. 7, 8 and 9 are schematic plan views of detonating cords inadjacent relation to each other as described herein.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

Detonating cords described herein comprise an outer sacrificial jacketwhich has the protective ability to prevent cut-off due to theinitiation of another length of detonating cord of the same or similarcore loading in contact therewith. Such a detonating cord can be usedunder conditions in which a section of the cord comes in contact with asimilar section of detonating cord (i.e., another section of the samecord or a section of detonating cord having a like core load ofexplosive material) without experiencing cut-off at the point ofcontact. This is achieved without the need to provide a jacket thatcompletely contains the explosive output of the core of the detonatingcord. Thus, the detonating cord exhibits some degree of brisance andmay, in fact, cause cut-off of a length of detonating cord notconfigured in accordance with this invention. Various embodiments ofdetonating cord described herein can be made without a metal jacketlayer in the interior jacket or in the sacrificial jacket, i.e., thecord may comprise a composite jacket that is substantially free of anymetal layer.

In addition, some embodiments of a detonating cord as described hereinmeet a cross-sectional outside diameter constraint that enables the cordto be capped, i.e., inserted into the shell of a standard-sizeddetonator having an inside diameter of about 1.3 mm (about 0.5 inch),without the need to strip any part of the jacket of the detonating cordbefore inserting it into the shell.

The subject detonating cords comprise a core of explosive materialsurrounded by a composite jacket having two components: an interiorjacket and an outer sacrificial jacket, both of which comprise one ormore jacket layers. The outermost layer (relative to the core) of theinterior jacket is in contact with the sacrificial jacket, which isdisposed thereon. Upon exposure to the brisance of an adjacent similarsection of detonating cord, the sacrificial jacket is broken and peeledaway from the interior jacket beneath it, but at least part of theinterior jacket and explosive core of the detonating cord remain intact,without having suffered cut-off, leaving the cord functional. In someembodiments, the sacrificial jacket comprises a sacrificial extrudedlayer comprising extruded polymeric material, which may be in directcontact with the interior jacket, or the sacrificial jacket mayoptionally further comprise additional sacrificial layers, such as asacrificial textile layer, within the sacrificial extruded layer and incontact with the interior jacket. Without wishing to be bound by anyparticular theory, it is believed that the fracture and peeling of thesacrificial jacket absorbs and diverts sufficient energy from theadjacent functioning detonating cord to preserve the integrity of theexplosive core and interior jacket therein, so that cut-off is avoidedand the utility of the remaining detonating cord is preserved.

To allow the sacrificial jacket to peel away from the interior jacket,the sacrificial jacket is not tightly bound to the interior jacket,i.e., the sacrificial jacket must be relatively easily separable fromthe adjacent outermost interior jacket layer. The sacrificial jacket canbe rendered separable from the interior jacket by several methods. Whenthe sacrificial jacket comprises a sacrificial extruded layer extrudeddirectly onto the interior jacket, adhesion between the two jackets canbe minimized to make the sacrificial jacket separable from the interiorjacket by cooling the outermost layer of the interior jacket beforeextruding the sacrificial jacket over it. Cooling can be achieved, inone embodiment, by passing the interior jacket through a cooling bathbefore extruding the sacrificial extruded layer onto it. This procedurefacilitates the use of a sacrificial extruded layer that comprises amaterial that is compatible with the material of the outermost interiorjacket layer. In another embodiment, a sample detonating cord wasprepared by slipping a sheath of polyolefin heat-shrink tubing having athickness of about 0.02 inch (about 0.5 mm) over a length ofpremanufactured, room-temperature detonating cord comprising anoutermost jacket comprising a blend of about 80 percent LDPE low densitypolyethylene) and about 20 percent HDPE (high density polyethylene)having an outer diameter of about 0.130 inch (about 3.3 mm). The sheathwas then heated sufficiently to shrink it onto the detonating cord.Alternatively (or, in addition) to cooling, the sacrificial extrudedlayer and the outermost interior jacket layer may comprise chemicallyincompatible or immiscible materials. Allowing for separation of anextruded jacket layer from one beneath it is contrary to standardpractice in the art because it is normally desired that each successiveextruded layer form a tight bond with the layer beneath it.

In other embodiments, the sacrificial jacket is made separable from theinterior jacket by providing a sacrificial jacket comprising asacrificial textile layer woven around the interior jacket and asacrificial extruded layer thereon. Even if the sacrificial extrudedlayer bonds tightly to the sacrificial textile layer, the sacrificialtextile layer will easily separate from the interior jacket layer aroundwhich it was woven. Therefore, when the sacrificial jacket functions,both the sacrificial extruded layer and the sacrificial textile layerseparate from the interior jacket.

One embodiment of such a detonating cord is illustrated in schematiccross section in FIG. 1. Detonating cord 10 comprises a core 12 ofexplosive material enclosed in a composite jacket comprising an interiorjacket 14 and a sacrificial jacket 20. Interior jacket 14 comprises atextile sleeve 16 and a surrounding extruded polymeric jacket layer 18.Optionally, core 12, sleeve 16 and jacket layer 18 may constitute alow-energy detonating cord, i.e., the interior jacket 14 may providesufficient tensile strength, water-resistance, etc., to provide, withoutsacrificial jacket 20, a commercially acceptable detonating cord inaccordance with the prior art. Adjacent to and surrounding the interiorjacket 14 is the sacrificial jacket 20 disposed thereon in accordancewith the present invention.

Core 12 may comprise any suitable explosive material; a typical corematerial comprises PETN. A detonating cord in accordance with thisinvention may have a core load of explosive material of less than about3.2 grams/meter (g/m), optionally in the range of about 0.2 to 2 g/m (1to 10 grains per linear foot (grains/ft)), optionally less than 1.25 g/m(6 grains/ft), e.g., from about 0.2 to 1.25 g/m (about 1 to 6grains/ft). In one optional embodiment, the detonating cord may have acore loading of about 1 to 1.5 g/m (about 5 to 7 grains/ft).

Textile sleeve 16 may comprise any suitable textile suitable formaintaining the lengthwise continuity of core 12. Providing a textilesleeve around a core of explosive material for use in detonating cord iswell-known in the art, as is the deposition of additional extruded andwoven layers thereon, such as extruded interior jacket layer 18.Alternatively, the innermost jacket layer may be extruded over the core.

Interior jacket layer 18 surrounding textile sleeve 16 is the outermostlayer of interior jacket 14. Interior jacket layer 18 may be a polymericmaterial extruded over textile sleeve 16. For example, jacket layer 18may comprise a blend of about 80 percent LDPE (low density polyethylene)and about 20 percent HDPE (high density polyethylene), as is well-knownin the art. In a particular embodiment, jacket layer 18 may have athickness of about 0.5 millimeter (mm) (about 0.02 inch), which isslightly less than the thickness of an outer jacket layer in acorresponding prior art device, which has a thickness of about 0.75 mm(about 0.03 inch) but which lacks an outer sacrificial jacket.

The sacrificial jacket 20 comprises a sacrificial extruded layerextruded over jacket layer 18. Optionally, sacrificial jacket 20 maycomprise a material that is chemically compatible or miscible with thematerial comprising jacket layer 18, e.g., sacrificial jacket 20 maycomprise the same kind of polymeric material comprising the interiorjacket layer on which it is disposed. For example, layer 18 and layer 20may both comprise polyolefins, e.g., a mixture of 80% LDPE and 20% HDPE.To reduce the bonding that would otherwise occur between two extrudedpolymeric layers of like materials, interior jacket layer 18 is allowedto cool before sacrificial outer jacket 20 is extruded thereon so thatthe sacrificial jacket 20 does not meld into or strongly adhere tointerior jacket layer 18. Cooling may be achieved by, e.g., passing theinterior jacket through a cooling water bath before sacrificial jacket20 is extruded thereon. The thickness of sacrificial jacket 20 is about0.25 mm (0.01 inch), e.g., from about 0.125 mm to 0.36 mm (about 0.005to 0.014 inch), optionally from about 0.2 to about 0.3 mm (about 0.008to 0.012 inch). In particular embodiments, the total outside diameter ofdetonating cord 10 may be not greater than about 3.8 mm (0.15 inch),e.g., in the range of from about 3.3 to about 3.8 mm (about 0.13 to 0.15inch), thus facilitating its use with a detonator having a standard sizedetonator shell, e.g., a No. 8 detonator shell having an inner diameterof about 6 millimeters (mm), e.g., 5.7 mm (about 0.22 inch).

In use, when a section of detonating cord 10 as shown in FIG. 1 isdisposed adjacent to a similar section of detonating cord, e.g., incrosswise relation to each other, the sacrificial outer jacket of thecord of this invention will prevent cut-off of that section of cordshould the other section of cord detonate. The mechanism by which thesacrificial outer jacket layer 20 functions is illustrated schematicallyin FIG. 2, where it is shown that at a point of contact, jacket layer 20has fractured and has separated from the interior jacket layer 18, whichremains intact.

In an alternative embodiment, jacket layer 18 may comprise a polymericmaterial that is incompatible with that of the sacrificial jacket layerin contact therewith, so that even if interior jacket layer 18 is notcooled before sacrificial jacket 20 is extruded onto it, jacket 20 willnot strongly adhere to layer 18, although cooling may optionally beperformed to enhance the separation of the sacrificial jacket from theinterior jacket. In another embodiment, the sacrificial jacket could bemade separable from the interior jacket by extruding the sacrificialjacket at a lower temperature than the interior jacket. The coolertemperature of the sacrificial jacket material inhibits intermingling ofthe polymeric materials of the sacrificial jacket and the interiorjacket. For example, a detonating cord may comprise a core of explosivematerial surrounded by an outmost interior jacket comprising SURLYN™polymer that may be extruded at 325° F. (about 163° C.) and asacrificial jacket comprising polyethylene (e.g., a blend of about 80%LDPE and about 20% HDPE) that may be extruded over the SURLYN™ polymerat about 300° F. (about 150° C.).

In yet another embodiment, the sacrificial jacket is rendered separableform the interior jacket therein by using a sacrificial jacket materialwhose melting temperature and/or extrusion temperature are significantlylower than the corresponding temperature(s) of the interior jacket layermaterial. The sacrificial jacket layer may then be extruded at a coolertemperature than the extrusion temperature of the interior jacket layer,so that the cooler temperature of the sacrificial jacket layer materialdiminishes its tendency to blend with the jacket layer 18 on which it isdisposed.

One specific embodiment of a method for producing detonating cordcomprising a sacrificial jacket as shown in FIG. 1 is depictedschematically in FIG. 3. According to this method, a source of yarn 28and a supply of pulverulent explosive 30 are provided to a firstprocessing station 32 where the yarn is woven into a textile sleeve 16(FIG. 1) about a core 12 of the explosive material. The resulting linearproduct is then passed to an extruder 34 (FIG. 3) where a polymericjacket layer 18 (FIG. 1) is extruded over the textile sleeve 16,yielding a detonating cord comprising an interior jacket 14 (whichcomprises sleeve 16 and layer 18) disposed around a core 12. Thedetonating cord is then passed to an optional cooling station 36 (FIG.3) which may comprise, e.g., a water bath, to cool layer 18 so that itresists adhesion by a subsequently extruded layer. The detonating cordthen passes to an extruding station 38 where a sacrificial jacket 20(FIG. 1) is applied over the interior jacket 14 to yield a detonatingcord 10 according to one aspect of this invention.

FIG. 4 depicts yet another embodiment of a method for producingdetonating cord, in which yarn 28 and explosive material 30 are providedto first station 32, from which the linear product comprising a core 12is encased in a textile sleeve 16 is passed to an extruder station 34.At extruder station 34, an interior jacket layer 18 is deposited thetextile layer 16 to produce a detonating cord comprising the core ofexplosive material 12 and an interior jacket 14 (which comprises sleeve16 and layer 18). The detonating cord then passes to an extrusionstation 44 where a sacrificial outer layer 20 is deposited over theinterior jacket to produce the detonating cord 10, without first beingpassed to a cooling station. In this embodiment, the sacrificial outerjacket 20 comprises a material that is incompatible with layer 18 andwhich is therefore easily separable therefrom.

An alternative embodiment of a detonating cord in accordance with thisinvention is shown in FIG. 5. Cord 10′ comprises a core 12 of explosivematerial enclosed in a composite jacket comprising interior jacket 14and a sacrificial jacket 22. Interior jacket 14 comprises a textilesleeve 16 and a surrounding extruded polymeric jacket layer 18.Sacrificial jacket 22 comprises a sacrificial textile layer 24 wovenabout interior jacket 14 and a sacrificial extruded layer 26 that hasbeen extruded directly onto the sacrificial textile layer 24. Thecomposite sacrificial jacket 22 is easily separable from interior jacket14 by virtue of sacrificial textile layer 24. Detonating cord 10′functions in substantially the same way as detonating cord 10.

One embodiment of a method for making detonating cord 10′ is depicted inFIG. 6, which illustrates that a source of yarn 28 and powderedexplosive material 30 that are passed to a first station 32 as describedwith reference to FIG. 5 to yield a linear product comprising a textilesleeve 16 disposed over a core 12 of explosive material. The linearproduct is then passed to an extruding station 34 where an inner jacketlayer 18 is applied to produce a detonating cord comprising an interiorjacket 14 (comprising sleeve 16 and interior jacket layer 18) disposedover core 12. The detonating cord then passes to a third station 40where a sacrificial textile jacket 24 is disposed over the interiorjacket layer 18. The cord then passes to an extrusion station 42 where asacrificial extruded layer 26 is extruded onto the sacrificial textilelayer 24, to which it may adhere. Together, the sacrificial textilelayer 24 and sacrificial extruded layer 26 comprise a sacrificial jacket22. As described above, the sacrificial textile layer 24 is easilyseverable from the interior jacket 14 on which it is disposed, thusenabling the removal of the entire sacrificial jacket 22 from thedetonating cord therein.

A section of a detonating cord comprising a sacrificial jacket asdescribed herein may be disposed in adjacent relationship to a similarsection of detonating cord and will survive the functioning of theadjacent section of detonating cord without experiencing cut-off. Suchadjacent relationships include side-by-side, generally parallelrelation, one embodiment of which being depicted, e.g., in FIG. 7;crosswise at an acute angle to each other, one embodiment of which beingdepicted in FIG. 8; or at right angles; and/or mutually twisted orintertwined dispositions, etc., as depicted, e.g., in FIG. 9, whether ornot the two sections of cord in any of such adjacent relationships arein actual contact or are merely in close proximity to each other.

In other alternative embodiments, the interior jacket of a detonatingcord may have a lesser or a greater number of layers than the interiorjacket of the illustrated embodiments.

Although the invention has been illustrated and described with respectto a single embodiment thereof, it would be recognized by one ofordinary skill in the art, upon a reading and understanding of theforegoing, that numerous alterations and variations to the disclosedembodiment fall within the spirit of the invention and the scope of thefollowing claims.

1. A detonating cord comprising: a core of reactive material and acomposite jacket around the core, the composite jacket comprising: aninterior jacket surrounding the core and in contact therewith andcomprising an outermost interior jacket layer; a sacrificial jacketdisposed over the interior jacket, the sacrificial jacket beingseparable from the interior jacket in response to the detonation of anadjacent similar section of detonating cord and being effective toprevent the cord from being cut off by the adjacent similar section ofdetonating cord.
 2. The detonating cord of claim 1 having a core load ofless than about 3.2 grams/meter (g/m) (15 grains/ft).
 3. The detonatingcord of claim 2 having a core load of less than 1.25 g/m (6 grains/ft).4. The detonating cord of claim 2 having a core load in the range ofabout 0.2 to about 2 g/m (1 to 10 grains/ft).
 5. The detonating cord ofclaim 4 having a core load in the range of from about 1 to about 1.5 g/m(5 to 7 grains/ft).
 6. The detonating cord of claim 1, claim 2 or claim4 wherein the outer cross-sectional diameter of the cord is not morethan about 3.8 mm (0.15 inch).
 7. The detonating cord of claim 1 orclaim 2 wherein the interior jacket is free of metal jacket layers. 8.The detonating cord of claim 1, claim 2 or claim 4 wherein thesacrificial jacket comprises a sacrificial textile layer woven over theinterior jacket and a sacrificial extruded layer extruded over thesacrificial textile layer.
 9. The detonating cord of claim 8 wherein thesacrificial extruded layer comprises a layer of polyethylene having athickness of about 0.25 mm (0.01 inch).
 10. The detonating cord of claim1, claim 2 or claim 4 wherein the sacrificial jacket comprises asacrificial extruded layer disposed directly onto the interior jacket.11. The detonating cord of claim 10 wherein the outermost interiorjacket layer and the sacrificial jacket comprise mutually compatiblepolymeric materials.
 12. The detonating cord of claim 11 wherein thesacrificial extruded layer and the outermost interior jacket layer bothcomprise polyethylene and the thickness of the sacrificial extrudedlayer has a thickness of about 0.25 mm (0.01 inch).
 13. The detonatingcord of claim 10 wherein the outermost interior jacket layer and thesacrificial jacket comprise mutually incompatible polymeric materials.14. A method for making a detonating cord, comprising: disposing aninterior jacket around a core of explosive material, the interior jacketcomprising at least an outermost interior jacket layer, the interiorjacket being insufficient to protect the detonating cord against cut-offby the initiation of an adjacent similar section of detonating cord; anddisposing a sacrificial jacket over the interior jacket.
 15. The methodof claim 14 comprising extruding the sacrificial jacket onto theinterior jacket, wherein the sacrificial jacket and the outermostinterior jacket layer comprise polymeric materials that are mutuallycompatible, and wherein the method comprises cooling the interior jacketbefore extruding the sacrificial jacket onto it.
 16. The method of claim14 comprising extruding the sacrificial jacket onto the interior jacket,wherein the sacrificial jacket and the outermost interior jacket layercomprise mutually incompatible polymeric materials.
 17. The method ofclaim 14 wherein disposing the sacrificial jacket around the interiorjacket comprises forming a sacrificial textile layer over the interiorjacket and extruding a sacrificial extruded layer onto the sacrificialtextile layer.